Singlet versus triplet dynamics of β-carotene studied by quantum control spectroscopy

Biomolecules very often present complex energy deactivation networks with overlapping electronic absorption bands, making their study a difficult task. This can be especially true in transient absorption spectroscopy when signals from bleach, excited state absorption and stimulated emission contribute to the signal. However, quantum control spectroscopy can be used to discriminate specific electronic states of interest by applying specifically designed laser pulses. Recently, we have shown the control of energy flow in bacterial light-harvesting using shaped pump pulses in the visible and the selective population of pathways in carotenoids using an additional depletion pulse in the transient absorption technique. Here, we apply a closed-loop optimization approach to β-carotene using a spatial light modulator to decipher the energy flow network after a multiphoton excitation with a shaped ultrashort pulse in the near-IR. After excitation, two overlapping bands were detected and identified as the S₁ state and the first triplet state T₁. Using the transient absorption signal at a specific probe delay as feedback, the triplet signal could be optimized over the singlet contribution.     

Tailoring a Zinc Oxide Nanorod Surface by Adding an Earth-Abundant Cocatalyst for Induced Sunlight Water Oxidation

Herein, a detailed investigation of the surface modification of a zinc oxide (ZnO) nanorod electrode with FeOOH nanoparticles dispersed in glycine was conducted to improve the water oxidation reaction assisted by sunlight. The results were systematically analysed in terms of the general parameters (light absorption, charge separation, and surface for catalysis) that govern the photocurrent density response of metal oxide as photoanode in a photoelectrochemical (PEC) cell. ZnO electrodes surface were modified with different concentration of FeOOH nanoparticles using the spin-coating deposition method, and it was found that 6-layer deposition of glycine-FeOOH nanoparticles is the optimum condition. The glycine plays an important role decreasing the agglomeration of FeOOH nanoparticles over the ZnO electrode surface and increasing the overall performance. Comparing bare ZnO electrodes with the ones modified with glycine-FeOOH nanoparticles an enhanced photocurrent density can be observed from 0.27 to 0.57 mA/cm² at 1.23 V_RHE under sunlight irradiation. The impedance spectroscopy data aid us to conclude that the higher photocurrent density is an effect associated with more efficient surface for chemical reaction instead of electronic improvement. Nevertheless, the charge separation efficiency remains low for this system. The present discovery shows that the combination of glycine-FeOOH nanoparticle is suitable and environmentally-friend cocatalyst to enhance the ZnO nanorod electrode activity for the oxygen evolution reaction assisted by sunlight irradiation.     

Production and Characterization of β-Glucanase Secreted by the Yeast Kluyveromyces marxianus

An extracellular β-glucanase secreted by Kluyveromyces marxianus was identified for the first time. The optimal conditions for the production of this enzyme were evaluated by response surface methodology. The optimal conditions to produce β-glucanase were a glucose concentration of 4 % (w/v), a pH of 5.5, and an incubation temperature of 35 °C. Response surface methodology was also used to determine the pH and temperature required for the optimal enzymatic activity. The highest enzyme activity was obtained at a pH of 5.5 and a temperature of 55 °C. Furthermore, the enzyme was partially purified and sequenced, and its specificity for different substrates was evaluated. The results suggest that the enzyme is an endo-β-1,3(4)-glucanase. After optimizing the conditions for β-glucanase production, the culture supernatant was found to be effective in digesting the cell wall of the yeast Saccharomyces cerevisiae, showing the great potential of β-glucanase in the biotechnological production of soluble β-glucan.     

Giant growth of quantum oscillations in an inhomogeneous 2D electron system

It is detected experimentally for the first time that the connection of 2D electron systems with different electrochemical potentials results in long-range (τ 50 μm) electron density disturbances. When a gated region of a Corbino sample is strongly depleted, the amplitude of the magnetoresistance oscillations caused by high density ungated regions is found to increase in direct proportion to the sample resistance, which is dominated by low-density regions with small conductivity. Experiments on samples with an artificial potential profile (antidots and etched rings) below the gate show that the observed effects are not due to contact effects. Pis’ma Zh. Eksp. Teor. Fiz. 63, No. 1, 55–60 (10 January 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Integrating nonlinear branch-and-bound and outer approximation for convex Mixed Integer Nonlinear Programming

In this paper, we present a new hybrid algorithm for convex Mixed Integer Nonlinear Programming (MINLP). The proposed hybrid algorithm is an improved version of the classical nonlinear branch-and-bound (BB) procedure, where the enhancements are obtained with the application of the outer approximation algorithm on some nodes of the enumeration tree. The two methods are combined in such a way that each one collaborates to the convergence of the other. Computational experiments with benchmark instances of the MINLP problem show the good performance of the proposed algorithm, which is compared to the outer approximation algorithm, the nonlinear BB algorithm and the hybrid algorithm implemented in the solver Bonmin.     

Thin zirconium nitride films prepared by plasma-enhanced CVD

Thin films of zirconium nitride have been deposited at temperatures as low as 573 K by PECVD using tetrakis(diethylamido)zirconium, Zr[N(C₂H₅)₂]₄ as precursor. The influence of the various experimental parameters on film properties and deposition rates has been studied. Under most experimental conditions hard coatings of good adherence and low carbon contamination resulted.     

Über den Einfluß von einwertigen Zwischenschichtkationen auf die elektrische Leitfähigkeit von Vermikulilten in verschiedenen Hydrationszuständen (Dielektrische Messungen an Schichtsilicaten IV (1, 2, 3))

Zusammenfassung An Vermikulitkristallen mit Li⁺ und Na⁺ als Zwischenschichtkationen in verschiedenen Hydrations-zuständen (trocken, isolierte Wassermoleküle und monomolekulare Wasserschichten) wurde der Realteil der dielektrischen Permeabilitätg und der dielektrische Verlustfaktortg im Frequenzbereich zwischen 30 Hz und 10 MHz gemessen. Die elektrische Leitfähigkeit in Richtung der Schichtnormalen wird sowohl vom Hydratwasser als auch (insbesondere bei niedriger Schichtladung) von der Natur der einwertigen Zwischenschichtkationen bestimmt: Bei niederen Frequenzen und niederen Hydrationszuständen dominieren Relaxationsphänomene auf Grund der Beweglichkeit dieser Kationen. Hingegen resultiert die Leitfähigkeit in den Stufen mit isolierten Wassermolekülen und mit monomolekularen H₂O-Schichten weitgehend aus einem Wanderungsmechanismus vonL-Defekten innerhalb der Wasserstrukturen, wie er bei Vermikuliten mit zweiwertigen Kationen nachgewiesen wurde.

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Summary The dielectric permeability s' and the dielectric losstg of vermiculite crystals with Li⁺ and Na⁺ as interlayer cations in different states of hydration (completely dehydrated, with isolated water molecules and with monomolecular water layers) were measured in the frequency range between 30 Hz and 10 MHz. The electrical conductivity normal to the silicate layers was determined by the influence of the hydrate water as well as especially in the case o£ low layer charge by the nature of the monovalent interlayer cations. At low frequencies and low states of hydration it could be interpreted by a relaxation process of the interlayer cations. With isolated water molecules and with monomolecular water layers the conductivity at higher frequencies was mainly determined by a mechanism of diffusion of structuralL-defects within the water layers as in the case of hydrated vermiculites with divalent cations.

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Mit 9 Abbildungen und 2 Tabellen     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.     

Hydrodynamics of dielectric fluid films

We introduce a general hydrodynamic model to study the stability of lipid films against thermal fluctuations. As one novel aspect the model accounts before all for a complete intrinsic surface rheology of the film interfaces. Thus the rheological behaviour of the surface adsorbed lipids is modelled which screen the hydrophobic film interior against the aqueous exterior. For coloured films we demonstrate first the influence of electrical forces on the dynamics and film stability. For that we perform a linear stability analysis on a simplified mechanically symmetric film with i) symmetric surface charge distribution and ii) linear electric potential drop across the film. Based on the complete film model we then categorize the complete set of solutions of the linearized equations of motion and we study the growth rates of unstable film modes. Finally we discuss the stability properties of a black film after introducing a repulsive mechanism due to the steric hindrance of the interfacial lipids.     

Theoretical study of the Raman cross section and its pressure dependence in silicon

Based on a pseudopotential calculation we predict the cross section for one phonon Raman scattering and its pressure dependence in Si. In the long wavelength regime our predictions differ markedly from earlier complete calculation but rather support results of a simple two band model. Hydrostatic pressure effects are demonstrated to be too small for an experimental assessment at the time being.